The proposed research focuses on two aspects of the regulation of gene expression which occur during the development and differentiation of erythroid cells in the chicken: 1) the isolation and characterization of non-globin genes whose products are specific for erythroid cell maturation and the nature of the control of expression of these genes; and 2) the pattern and products of expression of the most abundantly expressed genes in erythoid cells, the globin genes. The isolation of non-globin erythroid cell-specific genes will be accomplished by eDNA cloning of mRNA from erythroid cells. Two approaches are described. The first approach involves cloning of the entire non-globin mRNA population from erythroid cells and using labeled hybridization probes specific for mRNA of non-erythroid or erythroid cells to sort out those clones which are erythroid cell-specific. In the second approach, cDNA clones from non-erythroid cells will be prepared and the DNA will be hybridized in excess to mRNA from erythroid cells to selectively hybridized in excess to mRNA from erythroid cells to selectively hybridize those mRNA molecules common to both cell types. The unhybridized mRNA should be then substantially enriched in erythroid cell-specific sequences and will be cloned. Erythroid-specific cDNA clones will be identified by specific hybridization to erythroid cell mRNA. Once isolated, the cDNA clones will be used to follow the patterns of transcription and processing of these gene products during differentiation and to isolate and characterize the chromosomal sequences corresponding to these genes. The study of globin gene expression will be approached using transformation of erythroid cells by avian erythroblastosis virus (AEV), an avian retrovirus, to arrest the cells in particular stages of differentiation or development. By using chemical inducers or a viral mutant which is temperature-sensitive for transformation, this block can be removed, allowing a limited continued differentiation. The biochemical characterization of globin gene expression before and after induction will focus on the kinetics of RNA transcription and processing and the structure and cellular location of globin RNA using cloned globin mRNA or chromosomal DNA sequences as hybridization probes. In addition to studying globin gene expression, the AEV-transformed cell (Text Truncated - Exceeds Capacity)